Flap Wheel and a Method for Producing a Flap Wheel Having a Plate-Shaped Carrier

ABSTRACT

“The invention relates to a method for producing a flap wheel ( 4 ) having a plate-shaped carrier, wherein a plurality of grinding flaps ( 7 ) overlapping in a shingle-like manner are glued to an annular carrier section ( 3, 5 ) that is centered on a rotational axis A of the flap wheel ( 4 ), wherein the carrier section ( 3, 5 ) is produced from an amorphous thermoplastic material, in particular ABS, wherein the surface ( 8 ) of the carrier section ( 3, 5 ) is activated prior to gluing, a heat-curing adhesive is applied to the activated surface ( 8 ) of the carrier section, and the grinding flaps ( 8 ) are placed and pressed onto the carrier section ( 5 ) provided with heat-curing adhesive ( 7 ).”

The invention relates to a method for producing a flap wheel having a plate-shaped carrier, whereby a number of grinding flaps overlapping in shingle-like manner are glued onto an annular carrier section that is centered on the rotational axis of the flap wheel, whereby the carrier section is produced from an amorphous thermoplastic resin, in particular, ABS. Further, the invention relates to a flap wheel of the same type.

Known flap wheels have a flap carrier that typically consists of fabric-reinforced or fiber-reinforced plastics, or is constructed from unreinforced thermoplastic resin. The grinding flaps consisting of grinding material are glued overlapping shingle-like onto the surface of the carrier. As is known, the carrier section carrying the flaps is most often positioned perpendicular to the axis of rotation. To improve two-dimensional grinding—in a special type of the flap wheel—the carrier section is inclined so that the clamping screw virtually lifts off the surface to be finished when the inclined grinding surface bears on it.

When using a flap wheel, care must always be taken that the carrier and/or the adhesive lying under the grinding flaps does not come in contact with the workpiece. This leads to contamination or damage of the workpiece to be finished. As long as the grinding flaps glued to the carrier section protrude in the radial direction on the surface of the carrier, they securely guard the tool from coming in contact with the carrier. However, wear of the grinding flaps leads to shrinkage of the diameter of the flap wheel, so that the surface of the carrier appears under the grinding flaps. This is the reason why most of the time, only a third of the flap coating can be utilized in practice.

In practice, this disadvantage is addressed by grinding off the material protruding beyond the carrier by holding the rotating carrier to a suitable edge. This approach is known as trueing or trimming of the carrier

As the result of removing the protruding part by machining, grinding is possible again without having to worry about any contact of the carrier with the workpiece. In this manner, a significantly larger part of the flap coating can be utilized. It is known that in order to make defined trimming possible while retaining a cleanly machined carrier edge, instead of the fiber-reinforced plastics, thermoplastic resins, in particular amorphous thermoplastic resins such as ABS are used for the carriers.

However, to glue such carriers consisting of amorphous thermoplastic resin, only cold-curing adhesives consisting of two components have been used previously, as these adhesives ensure a particularly good purchase of the flaps on the carrier. But these adhesives have the disadvantage of a relatively low viscosity which is a contributing factor to a slight shifting of the freshly glued on grinding flaps upon an impinging mechanical load, or when stored improperly, if the adhesive has not thoroughly hardened. On the other hand, an adjustment to a sufficiently high viscosity is hardly possible, as the adhesive must be conveyed and mixed with the curing agent. Furthermore, the viscosity cannot be reduced to improve pumping and dosing by heating with a nozzle, because the increase in temperature would cause an acceleration of the hardening.

If a heat-curing system based on epoxy resin is used instead for gluing a carrier consisting of amorphous thermoplastic resin, the adhesive exhibits poor adhesion and consequently of the flaps on the carrier. This leads to a loosening of the glue layer and the flaps from the carrier, which results in a higher risk of accidents. Consequently, heat-curing adhesives have not been suitable for producing trimmable flap wheels up to now.

This poses the objective of providing a method for producing a flap wheel of the type cited at the beginning, in which the flaps can be fastened to the carrier in a simple and secure way. Beyond that, it is the objective of the invention to propose a flap wheel accordingly.

These problems are solved by a method having the features of Claim 1 and by a device having the features of Claim 6. Additional, particularly preferred embodiments of the invention are cited in the subordinated claims.

The important basic idea of the invention is to alter the surface of the carrier section prior to the gluing in such a way that a secure purchase is ensured, even of the heat-curing adhesive. This alteration is called activation and can be accomplished in various ways. When using the activation according to the invention, the heat-curing adhesive is applied to the activated surface of the carrier section. The grinding flaps are then placed on the carrier section provided with adhesive and pressed onto it.

The primary advantage lies therein, that activation improves the adhesion of the heat-curing adhesive on the surface of the carrier. Within the scope of the application, activation is to be understood as a mechanical, physical and/or chemical treatment, with the aid of which the surface is roughened, or is provided with a coating that improves the adhesion of the heat-curing adhesive. The roughening of the surface increases the available contact surface of the adhesive on the carrier section, the coating changes its properties. In addition, foreign bodies adhering to the surface are removed as a result of the activation. The activation increases the adhesion of the adhesive on the surface. By the activation according to the invention, the surface of the carrier consisting of ABS is prepared for the use of a heat-curing adhesive.

Consequently, the flap wheel according to the invention has a significantly higher minimum bursting speed value. For example, when the flap wheel has a diameter of 115 mm, the required minimum bursting speed value of 140/m/s is significantly exceeded. The conglutinated grinding flaps are retained securely on the activated carrier in spite of using a heat-curing adhesive. Moreover, a two-dimensional loosening of the adhesive from the carrier is no longer observed. In the case of an overload, only individual grinding flaps separate from the carrier section, which represents virtually no risk of injury.

Beyond that, using the heat-curing adhesive also offers significant advantages in the production process of the flap wheels. A heat-curing adhesive hardens significantly above room temperature, in particular, in a temperature range between 100 and 150° Celsius. The reaction of the adhesive and its reaction time depend on the temperature and can consequently be controlled by the temperature.

Consequently, in contrast to a cold-curing adhesive system, a heat-curing adhesive system can be inserted into the production process already mixed and ready-to use. A mixing chamber is no longer required. The viscosity can be adjusted with the help of, for example, fillers and/or or average molecular weight, and the required homogeneity, by the supplier already when the adhesive is produced, i.e. prior to processing.

Because of the relatively high heat tolerance, the desired viscosity of the adhesive can also be adjusted via the temperature. In this way, the heat-curing adhesive can be pumped and dosed without any problem. Due to the quick cooling on the flap carrier, the viscosity of the adhesive increases in a very short time, so that the flaps can be placed securely for handling [handlingsfest] and the glue does not run off on the carrier.

It is an additional advantage of heat-curing systems that these cannot harden in the components passing through them in the event of a longer stoppage of the production process. A time and cost-intensive exchange of these components, for example, a nozzle, after a stoppage of the production process, is consequently not required.

In a preferred embodiment, the activation of the surface of the carrier section takes place by slight grinding, partial chemical dissolving or slight etching. Each one of these activation methods can be automated easily and is therefore suitable for mass-producing flap wheels.

The activation of the surface according to the invention is preferably directly integrated into the production process. Activating the surface can be automated, so that in spite of the additional production step to be performed, a decrease of the level of production output can be avoided.

A very important advantage of the invention now lies therein, that by using the method according to the invention, a trimmable flap wheel with an inclined carrier section can be produced for the first time, because it is based on a thermoplastic resin. In it, the carrier section is inclined toward the axis of rotation of the carrier at an angle of between 50 and 85 degrees, in particular, between 60 and 80 degrees. This is now possible because the heat-curing adhesive has a sufficiently high viscosity with sufficient adhesive power during the processing stage, so that the flaps placed on it remain in their position and do not slide off the incline. Such flap wheels with an inclined carrier section have the significant advantage that the contact surface that is possible—and therefore the largest material abrasion—is especially large, because of the grinding surface that is inclined against the axis of rotation. As a result of the incline and the larger contact surface that is possible, the user of flap disks with an inclined geometry benefits from a significant added value.

By using an adhesive with high viscosity according to the invention, the individual grinding flaps can be retained securely for handling [handlingsfest] and it can be avoided that the adhesive runs off prior to hardening. In contrast to using a heat-curing adhesive according to the invention, the cold-curing adhesive that has been used previously to glue carriers consisting of ABS is not suitable for gluing grinding flaps on a flap carrier that is positioned at an incline.

In the following, various abrasive wear conditions of a flap wheel are described in FIGS. 1 to 5. Shown are:

FIG. 1 shows a schematic illustration of a carrier of a flap wheel with a straight carrier section;

FIG. 2 shows a schematic illustration of a carrier of a flap wheel with a carrier section aligned at an incline;

FIG. 3 shows a schematic illustration of a carrier aligned straight with a glued on grinding flap in new condition;

FIG. 4 shows a schematic illustration of a carrier aligned straight with a worn grinding flap;

FIG. 5 shows a schematic illustration with a carrier aligned straight with a trimmed carrier section.

FIG. 1 shows a schematic illustration of a straight carrier 1 of a flap wheel 2. Carrier 2 is located symmetrically around an axis of rotation A and has a straight carrier section 3, i.e. aligned perpendicular to the axis of rotation A. In FIG. 2, a carrier 4 with the same axis of rotation is shown which has an inclined carrier section 5—in the illustrated case—by approximately 70 degrees against axis of rotation A.

The various conditions of wear of a flap wheel with a trimmable carrier are shown in the additional figures on a straight carrier by way of example, but these are also applicable to a flap wheel with an inclined carrier section.

FIG. 4 shows a schematic illustration of a carrier 1 with a single grinding flap 8 glued onto surface 6 of carrier section 5 with adhesive 7. The still unused grinding flap 8 protrudes radially outward over surface 9 of carrier section 5. In the same way, it covers adhesive 7 located between it and carrier section 5. For finishing a workpiece, a section of the grinding flap is available that is outlined by arrows B and C.

In FIG. 5 after use, the grinding flap is worn extending over the area cited above up to the point marked with arrow. Adhesive 7 and carrier section 3 protrude radially at worn grinding flap 10. Some of adhesive 7 has already worn off. This poses the risk that upon further use of the flap wheel, the workpiece will also come in contact with surface 9 of protruding carrier section 3. To avoid this, carrier section 3 is trimmed. In this process, the parts of carrier section 3 and adhesive 7 that protrude at worn out grinding flap 10, are removed. FIG. 5 shows a carrier section 11 that is trimmed in this way. After removing those parts of carrier section 3 and adhesive 7 that protrude radially outward over worn out grinding flap 10, worn out grinding flap 10 again protrudes at the carrier section. Flap wheel 12 that is trimmed in this way can continue to be used. The process can be repeated as desired, so that the grinding flaps can be utilized over their entire grinding surface. 

1. A method for producing a flap wheel (4) having a plate-shaped carrier, whereby a number of grinding flaps (7) overlapping in shingle-like manner are glued onto an annular carrier section (3, 5) centered on an axis of rotation (A) of the flap wheel (4), whereby the carrier section (3, 5) is produced from an amorphous thermoplastic resin, in particular ABS, wherein the surface (6) of the carrier section (3, 5) is activated prior to being glued, that a heat-curing adhesive (7) is applied to the activated surface (6) of the carrier section, and that the grinding flaps (8) are placed onto the carrier section (5) to which heat-curing adhesive (7) has been applied and pressed onto it.
 2. A method as recited in claim 1 wherein the activation of the surface (6) takes place by slight grinding, partial chemical dissolution or slight etching.
 3. A method as recited in claim 1, wherein the activation of the surface (6) directly precedes the placement of grinding flaps (7) on it, and it is thus integrated into the process
 4. A method as recited in claim 1 wherein the heat-curing adhesive (7) is applied to the surface (6) of a carrier section (5), that is inclined to the axis of rotation (A) of the carrier (1) by between 50 and 85 degrees, in particular, between 60 and 80 degrees.
 5. A flap wheel (4), in particular produced by a method as recited in claim 1, having a plate-like carrier (1) that carries a number of shingle-like overlapping grinding flaps (8), whereby the grinding flaps (8) are glued onto a carrier section (3, 5), and whereby the carrier section (3, 5) consists of an amorphous thermoplastic resin, in particular ABS, wherein the grinding flaps (8) are glued onto the carrier section (3, 5) with a heat-curing adhesive (7).
 6. A flap wheel (4) as recited in claim 5, wherein the carrier section (5) is inclined to the axis of rotation (A) of the carrier (1) between 50 and 85 degrees, in particular between 60 and 80 degrees. 